Selenious acid compounds

Selenium dioxide. The compound is conveniently prepared by the oxidation of selenium with nitric acid, followed by dehydration of the selenious acid thus formed by cautious heating ... 

Discussion. This gravimetric determination depends upon the separation and weighing as elementary selenium or tellurium (or as tellurium dioxide). Alkali selenites and selenious acid are reduced in hydrochloric acid solution with sulphur dioxide, hydroxylammonium chloride, hydrazinium sulphate or hydrazine hydrate. Alkali selenates and selenic acid are not reduced by sulphur dioxide alone, but are readily reduced by a saturated solution of sulphur dioxide in concentrated hydrochloric acid. In working with selenium it must be remembered that appreciable amounts of the element may be lost on warming strong hydrochloric acid solutions of its compounds if dilute acid solutions (concentration <6M) are heated at temperatures below 100 °C the loss is negligible. 

Selenious acid, 24, 61, 62 Selenium, 24, 63 powdered, black, 24, 90 Selenium compounds, ease of oxidation, 24,91... 

Elemental selenium is not particularly irritating, but various compounds such as selenium oxychloride and selenium dioxide are strong vesicants. Skin contact with the fume of heated selenium dioxide caused an acute, weeping dermatitis, with the development of hypersensitivity in some cases. Selenium dioxide forms selenious acid when in contact with water if allowed to penetrate beneath the fingernails, it causes an especially painful inflammatory reaction. ... 

Compound 31, the synthesis of which is described in Section 10.09.9.2.3, undergoes a substantial rearrangement upon oxidation with selenious acid, giving 1,2,4-triazole 32 (Equation 6). A plausible mechanism for this transformation is presented in the original report <2003RCB1740>. 

Ferric salts are reduced to the ferrous condition and chromates are reduced to chromic salts. Salts of gold, silver, copper, antimony, bismuth and mercury are reduced to the free metals, which are frequently obtained as colloidal solutions if the original solutions are weak with the exception of the first-named there is a tendency for the liberated metal to be accompanied by sulphide, especially if excess of hydrosulphite is used.7 Chloroplatinic acid is reduced to red chloroplatinous acid solution. Tellurous and telluric acids, selenious acid and arsenic compounds, are reduced to the free elements.8... 

Certain selenium compounds exhibit bactericidal and fungicidal action,4 and selenious acid may be used as a herbicide against dandelion, Canada thistle and burdock. 

Many toning processes in photography involve the use of selenium compounds.6 One such process recently recommended consists in treating the print or lantern slide, after developing, fixing and washing, with a solution containing about 1 per cent, of crystalline sodium sulphide and 1 per cent, of sodium selenite or selenious acid after twenty minutes or so in such a bath intense brown tones are obtained with chlorobromide papers, or brown-violet tones with pure bromide papers.7... 

The reaction with the selenium compound is much more rapid than that with the sulphur compound. Some of the selenious acid becomes oxidised to selenie acid. When these selenium acids are treated with excess of hydriodic acid they become reduced to selenium ... 

If the oxychloride is applied in dilute benzene solution some nitrogen selenide or selenium nitride is also formed.3 With liquid ammonia in the presence of ether in open vessels, the primary product is the compound SeOCl2.4NH3, which is decomposed by water into selenium, selenium nitride, ammonium chloride, ammonium selenite and selenious acid in a sealed tube, selenium nitride is formed in comparatively good yield.4... 

Hydrogen sulphide reduces selenious acid solution with formation of a mixture of selenium and sulphur.13 The proportion of the two elements in the precipitate varies with the conditions. At one time this precipitate was regarded as a definite sulphide of selenium, but the sulphur can be entirely extracted by a mixture of benzene and carbon disulphide. The so-called sulphur selenide obtained by fusing together sulphur and selenium probably is also not a true compound, but only mixed crystals of the elements.14... 

Selenious acid forms a sparingly soluble crystalline additive compound with thiocyanic aeid, known as thiocyanoselenious acid, H2Se03.2HCNS. This is formed when a mixture of an alkali selenite and ammonium thiocyanate in aqueous solution is treated with fairly concentrated hydrochloric acid. When warmed with water it decomposes, liberating selenium.2... 

Dichloroselenoacetophenone, (C6H5.CO.CH2)2SeCl2,3 occurs when acetophenone (2 mols.) in dry ether reacts with selenium tetrachloride (1 mol.). The product crystallises in white needles, M.pt. 122° C., and is much more stable than the corresponding compound derived from acetone. It can be preserved without undergoing decomposition, but with dilute sodium hydroxide it yields acetophenone and selenious acid, more concentrated alkali causing the separation of selenium. With phenylhydrazine it gives a resinous mass. 

These compounds are formed by the interaction of o-diamines and sodium hydroselenite or selenious acid. 

The dihvdrochloride of 1 2-diamino-4-hydroxybenzene in aqueous solution is treated with the equivalent quantity of sodium hydroselenite in the same solvent. After a short time the product is filtered off and recrystallised from a large volume of water containing animal charcoal. It forms yellowish-brown needles, becoming red and sintering at 200c ., and melting with decomposition at 209° C. Its alkali solutions are red or yellow, according to the concentration. The compound is also obtained w hen 1 2-diamino-4-hydroxybenzene is treated with selenious acid. 

Sebacamic acid, methyl ESTER, 25, 71 Sebacamide, 25, 95 Sebacic acid, 25, 95 Sebaconitrile, 25, 95 27, 18 Selenious acid, 24, 61, 62 Selenium, 24, 63 27, 33 powdered, black, 24, 90 Selenium compounds, ease of oxidation, 24,91... 

Complex Uranyl Selenites.—A series of crystalline compounds, rich in selenious acid, have been prepared" by decomposing uranyl salts in solution by means of selenious acid or an alkali selenite. The products are yellow- in colour and insoluble in %vater. Compounds of the follow-ing composition have been prepared ... 

By dissoh-ing an alkali uranate in aqueous selenious acid, and allowing the solution to crj-stallise, the following compounds have been obtained ... 

While a, a -diphenylmethylenecyclopropane undergoes ring enlargement into 2,2-diphenylcyclobutanone upon treatment with selenious acid ", reaction of methylenecyclopropane with thallium(III) nitrate or mercury(II) hypochlorite leads mainly to ring fission products besides a low percentage (18 %) of cyclobutanone In addition to their formation by epoxidation of cyclopropylidene compounds, oxaspiropentanes are... 

Selenium dioxide, Se02 (mp 315 °C, sublimes), and selenious acid, H2Se03, which is obtained by the evaporation of an aqueous solution of Se02 [507, 50S], are very selective oxidants. They are capable of mild dehydrogenation to form double bonds [375] and can oxidize alkenes and acetylenes to vicinal dicarbonyl compounds [509, 510] and allylic ethers to aldehydes [511]. The most important applications are conversions of alkenes into allylic alcohols [5i2] of benzylic, methyl, or methylene groups into carbonyl groups [513, 514, 5i5] and of carbonyl compounds into a-... 

Methyl and methylene groups adjacent to carbonyl groups are easily oxidized to carbonyls to yield a-keto aldehydes or a-diketones. The reagent of choice is selenium dioxide or selenious acid. The reaction is catalyzed by acids and by acetate ion and proceeds through transition states involving enols of the carbonyl compounds [518]. The oxidation is carried out by refluxing the ketone with about 1.1 mol of selenium dioxide in water, dilute acetic acid, dioxane, or aqueous dioxane [517]. The byproduct, black selenium, is filtered off, but small amounts of red selenium sometimes remain in a colloidal form and cannot be removed even by distillation of the product. Shaking the product with mercury [523] or Raney nickel [524] takes care of the residual selenium. The a-dicarbonyl compounds are yellow oils that avidly react with water to form white crystalline hydrates (equations 407 and 408). 

Removal of selenium and selenious acid. Use of selenium dioxide or selenious acid as an oxidant is attended with the difficulty of freeing the reaction mixture of colloidal selenium and of excess oxidant. A procedure for the oxidation of paraldehyde to glyoxal and isolation of the product as the bis-bisulfite addition compound specifies use of lead acetate as more satisfactory for the removal of selenious acid than sulfur dioxide, provided that the solution is kept cool and a large excess is avoided. A... 

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